Alabama's Snow Forecast-- What went wrong?

Jan 29, 2014

Alabama's monster snowstorm that paralyzed cities and left motorists stranded on highways has given weather forecasters a lot to think about. Tuesday's weather outlook called for snow south of Interstate twenty, impacting cities like Montgomery, Selma, and Mobile. By mid-morning, snow was blanketing Tuscaloosa and Birmingham, prompting immediate traffic gridlock that turned into a weather emergency. Alabama Public Radio's Pat Duggins spoke with Renny Vandewege about it. He teaches broadcast meteorology at Mississippi State University. Vandewege says snow is difficult to forecast, and weather watchers failed to factor in the cold weather in Alabama before the snow hit, which caused the roads to freeze faster...

Renny Vandewege: As meteorologists, we need to understand that we’re not just forecasting the weather conditions, but we also need to forecast the impacts that those conditions can cause towards the public. That includes road conditions; we need to actually try to forecast how the road is going to change throughout the day. As a meteorologist, that isn’t something you necessarily learn in a classroom. Really it’s just through time. It takes experiencing how weather has direct impacts on things like infrastructure and road conditions, so that in the future, when we do get an event, somewhere to yesterday, we have a sense of that will do to the roads and the problems it can cause.

Pat Duggins: I know it’s super early to ask this, but, you know, just from your own experience, what do you think went wrong yesterday?

Renny: The problem, well I guess, what went wrong is the fact that this has been a unique winter in the south, in that this isn’t just our first big arctic blast, but it’s our second, or even third arctic blast. And that causes the road conditions, and most of the ground is even frozen or it doesn’t take much cold to get it frozen. And so the snow that fell yesterday accumulated extremely quickly; and normally we’ve had one, two or three inches of snow that’s fallen, and it hasn’t done anything to the roadways. But yesterday, with the roads already being cold, putting snow on top of that meant it was going to stay immediately. And that meant that the conditions deteriorated just as quickly as the snow fell, and I think that we went from good roads to bad roads almost immediately, and it caught people off guard.

Pat: Do you think that the meteorology world, in general, is kind of taking notes, saying “Okay, you know, next time we have like several arctic vortex blasts and then we have the possibility of snow fall, this is probably going to happen?” They’re kind of rewriting the rule book?

Renny: Yeah, well if we aren’t taking notes, we should be, because as a meteorologist, you have to have humility and understand that when you think you have it all figured out, you don’t. And the atmosphere can humble you really quickly. So good meteorologists always journal either in their minds, or even on paper what went right and what went wrong, so that the next time you face a similar situation, you’re more prepared, and therefore, you can make the public and decision makers more prepared.

Pat: So, again, I mean obviously I’m not a trained meteorologist here, we were talking earlier about the movement of the Gulf of Mexico, and how that could, like you know, push the snow line by fifty or a hundred miles. For someone who is not a black belt in this, how did that happen? How does that work?

Renny: Well, there’s a, again it is complicated, so I’ll do my best to make this understandable. But when you’re tracking world pressure, in a rain situation, we’re talking about the difference, as it pertains to rain, of one-tenth of an inch of rain versus two-tenths of an inch of rain. And if you deal with rainfall, that’s virtually unnoticeable, unless you have a rain gauge. When that becomes a snowflake, the snow accumulates at a ratio of about ten to twenty inches, in snowfall, per one inch of rainfall. So our one-tenth of an inch of water, all the sudden, became not one inch of snow, but it became two or three inches of snow. And that’s where the impact of the snow forecast is so dramatic; that’s a minute detail that is very hard to pinpoint, and so the track of the low pressure then determines where that precipitation is going to fall, and in this case, when you’re dealing with snow, a fifty-mile difference means a dusting of snow or three inches of snow. And really probably the first to admit that the science of meteorology just isn’t good enough; there’s so many uncertainties that exist in the atmosphere that it is hard for us to get that track of a low to within fifty miles, and knowing, you know, where we think that’s going to fall. Sometimes we get it right, and, in fact, most of the times I think we do a pretty good job, but then you get that one time where you’re fifty or a hundred miles off, and it causes gridlock and really a disaster, in this case.